A fundraising specialist says three-quarters of the money raised for charities by telemarketing companies is typically spent covering call centre costs.
Epilepsy New Zealand, which provides services for sufferers, has cut ties with fundraising body, the Epilepsy Foundation, over the issue.
Although it received almost $3 million in donations via telemarketing in the past three years, Epilepsy New Zealand says more than 20% went on running the foundation's office and 75% was absorbed by telemarketers.
Heather Newell, who publishes Fundraising New Zealand, says that proportion is the norm.
She advises the use of telemarketing mainly to contact potential new donors, rather than maintaining a relationship with existing ones.
Asthma New Zealand says it does not use telemarketing because the cost is immense.